1. Field of the Invention
The present invention relates to a fuel injection control device and a fuel injection control system for controlling an operation of an injector such that fuel to be injected into a combustion chamber per combustion cycle is divided and injected through multiple times of injections.
2. Description of Related Art
There is conventionally known a fuel injection control device that controls an operation of an injector such that fuel to be injected into a combustion chamber per combustion cycle is divided and injected through multiple times of injections. For example, a technology described in each of Patent document 1 (JP-A-H11-148410) and Patent document 2 (JP-A-H11-141386) performs an injection of a small quantity of fuel through a pilot injection (first injection) prior to a main injection (second injection). The pilot injection exerts following effects (1) and (2).
(1) Since combustion of the fuel injected by the pilot injection (referred to as pilot combustion hereinafter) occurs before combustion of the fuel injected by the main injection (referred to as main combustion hereinafter), temperature of a wall surface of a combustion chamber is increased before start of the main combustion. In consequence, an ignition delay of the main combustion is inhibited to reduce a combustion noise.
(2) Since a premixed gas formed by the pilot injection burns in an early stage of the main combustion, an injection quantity to be injected by the main injection can be reduced. In consequence, combustion gas temperature can be reduced to reduce a production of NOx.
The technology described in Patent document 1 estimates an injection quantity actually injected by the pilot injection and controls the pilot injection such that a deviation between the estimated injection quantity and a target quantity becomes zero. In the estimation, change of cylinder pressure attributable to the pilot combustion is sensed with a cylinder pressure sensor, and a heat production Iq (shown by a shaded area in part (b) of FIG. 5) by the pilot combustion is calculated based upon the sensing result. Then, a pilot injection quantity is estimated based upon the calculated heat production Iq.
However, since the pilot injection quantity is much smaller than the main injection quantity, the change in the cylinder pressure (change in the heat production Iq) caused by the pilot combustion is extremely small. Therefore, high accuracy is required of a cylinder pressure sensor to estimate the pilot injection quantity with high accuracy, leading to an increase of cost.
In a multistage injection (referred to as multi-injection, hereinafter) of dividing a fuel quantity and performing injection of the divided fuel quantity in multiple times during a combustion cycle, the fuel quantity injected through each injection is small. Therefore, not only for the pilot injection exerting the above-described effects (1) and (2) but also for other injections, high accuracy is required of the cylinder pressure sensor in order to estimate the injection quantity as described above.